In recent years, a wireless power-transmitting system which wirelessly transmits electric power by making a power-transmitting coil and a power-receiving coil face each other has attracted attention. That is, in recent years, a wireless power-transmitting system has been known in which a coil on the power-supplying side (a power-transmitting coil) is installed on the ground or buried so as to be flush with the surface of the ground, and an electric vehicle provided with a coil on the power-receiving side (a power-receiving coil) is stopped above the power-transmitting coil, and thus electric power is wirelessly supplied from the power-transmitting coil to the power-receiving coil.
The wireless power-transmitting system adopts a magnetic field resonance method or an electromagnetic induction method, and application to the power transmission of a vehicle such as an electric vehicle is expected. However, in the wireless power-transmitting system, if a foreign object exists between the power-transmitting coil and the power-receiving coil, power-transmitting efficiency falls, and if the foreign object is metal such as an empty can, there is a possibility that heat may be generated under the influence of a magnetic field.
That is, if a foreign object composed of an electrically conductive body or a magnetic body such as metal enters between the power-transmitting coil and the power-receiving coil of an automobile (a vehicle), an eddy current is generated in the foreign object, and thus the temperature of the foreign object rises due to Joule heat generation. Then, the temperature of the power-transmitting coil also rises according to a rise in the temperature of the foreign object. Further, a magnetic field which the power-transmitting coil generates is weakened by the foreign object, and therefore, the transmission (power transmission) efficiency is considerably reduced.
Patent Document 1 discloses a power-transmitting device provided with a power transmission part which transmits electric power by using a magnetic field, and a foreign object removing operation part which removes a foreign object in the vicinity of a power transmission path of the electric power transmission. The foreign object removing operation part removes the foreign object by using at least one operation of the tilt, the rotation, and the vibration of an accommodation part which accommodates the power transmission part.
Patent Document 2 discloses an electric vehicle provided with a sweeping part which sweeps out a foreign object which already exist on a power-transmitting coil before the start of charging. The sweeping part is disposed on the bottom surface of the electric vehicle, is made to be movable between an accommodated state and a sweepable state, and moves to the sweepable state when the electric vehicle has approached a power-supplying part.
Patent Document 3 discloses an electric machine system provided with a domed housing which prevents an animal or a foreign object from being placed on a ground-installed transducer. The domed housing includes an outer surface having a plurality of points disposed at a plurality of heights, in which at least one of the plurality of points has a first height and other points of the plurality of points have the respective heights lower than the first height.
Further, in, for example, Patent Document 4, a charging device which has a charging surface made so as to be an inclined surface having an angle with respect to a horizontal plane or a vertical surface and prevents heat generation due to a foreign object is known.
Patent Document 5 discloses a wireless power-transmitting system in which at least one of a power-transmitting coil and a power-receiving coil is covered with an openable and closable winding-type roll screen, and thus the surfaces (operation surfaces) of the power-transmitting coil and the power-receiving coil are prevented from becoming dirty.
Patent Document 6 discloses a wireless power-transmitting system in which a foreign object placed on an upward convex conical member which covers a power-transmitting coil and is formed so as to come into close contact with a member covering a power-receiving coil, by moving upward at the time of wireless power transmission, falls along a slope of the conical shape according to the movement of the power-transmitting coil.
Patent Document 7 discloses a wireless power-transmitting system in which if the existence of a foreign object on a power-transmitting surface is detected during wireless power transmission, an electric current having a specific frequency is supplied to one of two power-transmitting coils and thus two different variation magnetic fields by two electric currents having different frequencies are generated from the two power-transmitting coils, and as a result, the power-transmitting surface vibrates at a third frequency.
Patent Document 8 discloses a device that cleans a lens or a CCD by driving a brush by alternately bending a polymer actuator from side to side.
Patent Document 9 discloses a paper transport device with a foreign object sticking prevention function which vibrates a transport roller by using a super-magnetostrictive element, and an image forming device provided with the paper transport device.